1. Field of the Invention
The present invention relates to identifying the optical fibers of an optical fiber composite overhead ground wire (OPGW) made of a ground wire and the optical fibers.
2. Background of the Invention
An optical fiber composite overhead ground wire is shown in FIG. 1 and comprises optical fiber units 20 (each made of one or more optical fibers). A grooved spacer 21 made of aluminum or plastic contains the optical units 21. The spacer is contained in an aluminum tube 22. Aluminum wires or aluminum-coated steel wires 23 are wound on the aluminum tube 22.
For example, six optical fibers of an optical fiber composite overhead ground wire are included in each of two optical fiber units and are laid on a central tension member 30 as shown in FIGS. 2, 3 and 4. Each of the twelve resultant optical fibers is conventionally identified by one of the three following methods.
(1) Twelve different colors 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12 are provided on the twelve optical fibers, as shown in FIG. 2, for identification. This is an all-color differentiation system. PA1 (2) The two optical fiber units are identified by the difference between colors 2 and 3 of fibers contained respectively therein, as shown in FIG. 3. The remaining optical fibers of each of the optical fiber units are identified by counting in the direction of 1 to 2 and 1 to 3. This is a tracer system. PA1 (3) The mutually-corresponding optical fibers of the two optical fiber units are provided with the same colors 1 through 6 and the two units are identified by tapes or sheaths 31 having .different colors and wound or fitted on the units, as shown in FIG. 4. This is the unit color differentiation system.
In the all-color differentiation system, it is easy to identify the optical fibers but twelve colors are needed, thus increasing the cost.
In the tracer system, only four colors are needed for all the optical fibers and therefore this system yields a lower cost. However, it is inefficient to identify and count the optical fibers in field work because the diameter of each of the optical fibers is as small as 0.25 to 0.9 mm and the same color 4 is used for a large number of optical fibers.
In the unit color differentiation system, it is not inefficient to identify the optical fibers because the optical fiber units are identified by the different colors and the optical fibers of each of the units are then identified by different colors. However, since the tapes or sheaths 31 having the different colors are provided, the number of manufacturing steps and the cost of the cable are increased.
Although the unit color differentiation system is adopted for most of optical fiber composite overhead ground wires now, the system has the above-mentioned problems which increase the number of manufacturing steps and the cost of the cable.